ΔE 20.7, loose: different enough that you should pick on purpose. Light Violet is noticeably darker, cooler than Lilac.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Light Violet is noticeably darker, cooler than Lilac.
The same difference applies the other way round: Lilac is noticeably lighter, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Lilac on the colour wheel See Light Violet on the colour wheel
All matches: Lilac equivalents · Light Violet equivalents